Temporal dynamics of the medial olivocochlear reflex in humans

Abstract

Ipsilateral and contralateral sounds can activate the medial olivocochlear reflex. The time course of medial efferent effects could contribute to the binaural unmasking of sounds. Computational modeling suggests that implementing efferent time constants improves speech-in-noise recognition. In addition, the time course could also support the protective function offered by the medial efferents. However, the current knowledge of efferent time constants is limited to a few probe frequencies (e.g., 1000 Hz) in limited subjects. The time course of medial efferent activation might be different for other probe frequencies or elicitors. In this study, the time course of the medial olivocochlear reflex was measured using stimulus frequency otoacoustic emissions recorded at spectral peaks near 1000 and 4000 Hz with broadband elicitors in 17 normal-hearing adults. Several preliminary but important findings emerged: (1) The onset response could be fitted with fast, medium, and/or slow time constants for limited subjects; (2) The magnitude (30–40%) of the efferent effect was similar to those reported in the literature; (3) The overall decay time appears to be longer for 4000 Hz relative to 1000 Hz; and (4) There was large individual variability in all response parameters across subjects. These findings will be discussed in detail. [Work supported by NIH/NIDCD R01DC018046.]